add flake, envrc

flake.nix

@@ -1,36 +1,37 @@
 {
-  description = "Rust Development Shell";
+  description = "Pinned Rust dev shell";
 
   inputs = {
-    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     rust-overlay.url = "github:oxalica/rust-overlay";
-    flake-utils.url  = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, rust-overlay, flake-utils, ... }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs = { self, nixpkgs, rust-overlay, ... }:
+  let
+    systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+    forAllSystems = f: nixpkgs.lib.genAttrs systems (system:
       let
-        overlays = [ (import rust-overlay) ];
         pkgs = import nixpkgs {
-          inherit system overlays;
+          inherit system;
+          overlays = [ (import rust-overlay) ];
         };
-      in
-      with pkgs;
-      {
-        devShells.default = mkShell {
-          buildInputs = [
-            openssl
-            pkg-config
-            (
-              rust-bin.selectLatestNightlyWith (toolchain: toolchain.default.override {
-                extensions = [
-                  "rust-src"
-                  "rust-analyzer"
-                ];
-              })
-            )
-          ];
+        rustToolchain = pkgs.rust-bin.stable."1.89.0".default.override {
+          extensions = [ "rust-src" "rust-analyzer" ];
         };
-      }
+      in f pkgs rustToolchain
     );
+  in {
+    devShells = forAllSystems (pkgs: rustToolchain: {
+      default = pkgs.mkShell {
+        nativeBuildInputs = [
+          pkgs.pkg-config
+          rustToolchain
+          pkgs.lldb
+        ];
+        buildInputs = [
+          pkgs.openssl
+        ];
+      };
+    });
+  };
 }